1,1,1-trichloroethane (methylchloroform) has become a promising solvent for the metal working and textile industries because of its low toxicity and good ecological properties and is being widely used by industry to replace both trichloroethylene and perchloroethylene. However, 1,1,1-trichloroethane is known to exhibit a high degree of instability in the presence of aluminum, and/or iron and/or copper and/or their alloys and when certain inhibitors are present to increase stability, then often zinc becomes a problem.
The art in some ninety odd U.S. patents alone discloses literally hundreds of compounds as exhibiting some inhibiting effect on 1,1,1-trichloroethane in the presence of metals and acids, principally the inorganic acid hydrogen chloride. The early stabilizers such as tertiary butyl alcohol which prevented rapid deterioration of 1,1,1-trichloroethane in the cold but was substantially ineffective when the solvent was used hot, and secondary butyl alcohol which was employed as a storage stabilizer to prevent discoloration from contact during storage in iron drums, gave way quickly to 1,4-dioxane alone and in combination with non-primary alcohols which rapidly broadened the areas of use into which this solvent could be safely employed. This stabilizer system was disclosed in U.S. Pat. No. 2,811,252. Shorly after introduction of 1,4-dioxane it was disclosed in U.S. Pat. No. 2,923,747 that nitromethane could contribute to the stabilization when used in combination with 1,4-dioxane. Ultimately, epoxides were found (U.S. Pat. No. 3,049,571) to enhance even the 1,4-dioxane and nitromethane as well as the non-primary alcohols. The advent of this latter discovery opened the way to cautious usage of 1,1,1-trichloroethane in vapor degreasing. Other commercial compositions began to find their way into the marketplace until today some five additional 1,1,1-trichloroethane compositions are on the market.
These compositions contain (a) 1,3-dioxolane, nitromethane, butylene oxide, isobutyl alcohol and toluene; (b) butylene oxide, acetonitrile, trioxane and nitromethane; (c) tertiary butyl alcohol, nitromethane and methyl butynol; (d) butylene oxide, tertiary amyl alcohol, methyl ethyl ketone, and nitromethane; and, (e) nitromethane, acetonitrile, butylene oxide and isopropyl nitrate. Thus, commercially only a few of the literally hundreds of compounds disclosed in the patent literature are useful under the stringent industrial conditions.
To establish the state of the art at the time this invention was made, a Table is hereafter set forth detailing in tabular form the patent literature most closely related to the present invention. TBL3 2,811,252 2,933,747 3,049,571 3,000,978 3,070,634 3,099,694 3,113,156 3,265,747 3,238,137 Methyl ethyl ketone Trimethylorthoformate Alkyl cyanide Monoolefin X Toluene Nitriles Furans Ethyl acetate Oxazole Amines 1,2-dimethoxy ethane Perchloroethylene X Nitroalkanes (nitromethane) X X Dioxadiene Dioxene Trioxane X X Dioxolane X Dioxane X X X X Butylene oxide/oxiranes X X X X X X Acetylenic alcohols O X /X* Secondary alcohols O X X /X /X Tertiary alcohols O /X /X Primary alcohols /X N-methyl pyrrole 3,251,891 3,326,988 3,326,989 3,360,575 3,397,148 3,445,523 3,505,415 3,532,761 3,549,715 3,564,061 3,665,747 3,676,355 Methyl ethyl ketone Alkoxy /X Trimethylorthoformate Group X Alkyl cyanide + /X Monoolefin X any Toluene of Nitriles X X list /X /X Furans X Ethyl acetate Oxazole X Amines /X X 1,2-dimethoxy ethane X X Perchloroethylene X Nitroalkanes (nitromethane) X X X /X /X X /X X Dioxadiene Dioxene /X Trioxane X /X Dioxolane X X /X Dioxane /X /X /X /X X Butylene oxide/oxiranes X X X /X X /X X /X X /X Acetylenic alcohols /X /X /X /X /X /X /X Secondary alcohols /X /X /X /X /X /X /X /X Tertiary alcohols /X /X X /X /X /X /X /X Primary alcohols /X /X /X /X Oxetane /X /X /X N-methyl pyrrole X *A slash line (/) before an X means the component is optional or merely suggested as a possible additional component.
It is apparent from the above Table that while many of the compounds and mixtures of compounds are capable of preventing the aluminum reaction in the laboratory tests, they are not widely used in commercial applications because of cost, availability, toxicity, loss through evaporation when the compositions are heated in use, etc. It is with such lists of compounds and their shortcomings in mind that the present invention was made.
The criteria for establishing a commercial grade of 1,1,1-trichloroethane which has unrestricted utility in industry should include an equal degree of stability of the liquid and its vapors, less than about ten (10%) percent total inhibitors and a substantial ability to be distilled without loss of stability by concentration of the low boilers in the overhead and their subsequent loss from the system and high boilers in the bottoms of the still through improper or inefficient still operation, and the like. Even today these criteria are not all found in the commercial compositions.
The compounds which are combined in accordance with the present invention have been disclosed in the art and in some instances have been used commercially. However, each lacks one or more properties which requires its combination with one or more compounds which also lack some other property required; thus, the necessity to balance a stabilizer composition. To demonstrate this phenomenon, the compounds combined in accordance with the present invention are each set forth with the property or properties they lack as stabilizer components.
__________________________________________________________________________ 1 2 3 DIOXANE DIOXOLANE TRIOXANE CH.sub.3 NO.sub.2 TBA BO __________________________________________________________________________ High boiling -- -- build-up in sump Excessive loss to -- -- -- vapors Zinc attack -- -- -- -- Inadequate protection -- -- -- -- -- in presence of Al- copper containing alloy (2024 Al) in both phases Loss in presence of -- iron and water Loss to vapor -- -- -- build-up in sump -- -- Order of activity 1 4 2 3 5 6 to 1100 Al __________________________________________________________________________ 1 - Nitromethane 2 - t. butyl alcohol 3 - Butylene oxide
To demonstrate the significance of order of activity with respect to 1100 aluminum the equivalency of each compound, i.e., the least amount of the compound required to prevent attack on 1100 aluminum in either phase is set forth:
______________________________________ wt. % 1.6* 2.6 3.1 dioxane .congruent. trioxane .congruent. nitromethane .congruent. 4.0 4.2 9.8 dioxolane .congruent. t. butyl alcohol .congruent. butylene ______________________________________ oxide *(Waring Blendor test APHA color index &lt;1000).
If further these compounds are compared as to the minimum amount required in an initial charge of solvent to stabilize both top and bottom after partitioning (50% by volume overhead), the following is obtained:
______________________________________ wt. % 3.4 4.4 4.4 dioxane .congruent. nitromethane .congruent. dioxolane .congruent. 5.0 8.2 12.2 trioxane .congruent. t. butyl alcohol .congruent. butylene ______________________________________ oxide
Thus, it becomes apparent a major balancing is required but even this data with the prior art disclosures fails to teach or suggest what balance is required with what compounds. It is therefore an object of this invention to provide compositions which are effective at concentrations of from between about four (4%) percent to about six (6%) percent and which meet the criteria set out above.